congratulations on the PocketBeagle: a nice cute design, we are taking a close look at it just now, to see what's been left behind squeezing down the form factor.
0x840, which does not seem to be broken out on the PocketBeagle. P8.15 (the line just above it!) is on P2.20. So I think P9.15 is missing. That is used as a GPIO which is the CS for the SPI ADC I think, so there may be options for re-routing it. As far as I can tell from our schematics, SPI_DAC_CLR is not in use. It can be connected in order to asynchronously clear the DAC output, but at the moment it sinks into the level shifter and then goes to the DAC chip through a DNI resistor, so it's basically unused.
PS: Derek Molloy's pdf pinout for the BBB has been a great tool over the years, hope to see something similar appear soon for the PB. Actually, an interactive, "universal" one - along the lines of the one you posted above - would be very powerful at this stage, with the proliferation of so many different boards / SoCs / SiPs !